Interesting study by IATA on the world's busiest passenger routes in 2013.

1. Hong Kong to Taipei -- 4,876,5952. Dublin to London -- 3,562,9513. Jakarta to Singapore -- 3,435,3754. Seoul to Tokyo -- 3,272,3755. London to New York -- 2,729,3626. Amsterdam to London -- 2,724,0227. London to Milan -- 2,075,4858. Honolulu to Tokyo -- 1,895,6119. New York to Toronto -- 1,600,22610. New York to Paris -- 1,545,938